Optical waveguide sheet, backlight unit, and portable terminal

ABSTRACT

An optical waveguide sheet for use in an edge-lit backlight unit is provided, that allows rays of light to enter the end face and emits the rays of light from the front face substantially uniformly. The optical waveguide sheet includes on the back side thereof: a sticking preventive means; and a plurality of recessed portions falling toward the front face side. The sticking preventive means: a plurality of annular raised portions each provided around each of the plurality of recessed portions and projecting toward the back face side; and a plurality of protruding portions provided scatteredly in a region which does not include the annular raised portions. The optical waveguide sheet is preferably for use as a light guide film having an average thickness of no less than 100 μm and no greater than 600 μm.

FIELD OF THE INVENTION

The present invention relates to an optical waveguide sheet, a backlightunit, and a portable terminal.

BACKGROUND OF THE INVENTION

Liquid crystal display devices in widespread use have been in abacklight system where light emission is executed by illuminating aliquid crystal layer from the rear face. In this system, a backlightunit such as edge-lit backlight unit or a direct-lit backlight unit ismounted on the underside of the liquid crystal layer. As shown in FIG. 7a, such an edge-lit backlight unit 110 generally includes a reflectionsheet 115 disposed on the front face of a top plate 116, an opticalwaveguide sheet 111 disposed on the front face of the reflection sheet115, an optical sheet 112 disposed on the front face of the opticalwaveguide sheet 111, and a light source 117 that emits rays of lighttoward the end face of the optical waveguide sheet 111 (see JapaneseUnexamined Patent Application, Publication No. 2010-177130). In theedge-lit backlight unit 110 shown in FIG. 7 a, rays of light that havebeen emitted from the light source 117 and have entered the opticalwaveguide sheet 111 propagate through the optical waveguide sheet 111. Apart of the propagating rays of light exit from the back face of theoptical waveguide sheet 111, are reflected on the reflection sheet 115,and enter again the optical waveguide sheet 111.

In liquid crystal display devices having such a liquid crystal displayunit, in order to enhance its portability and user-friendliness, areduction in thickness and weight is required, leading to a requirementalso for a reduction in thickness of the liquid crystal display unit. Inparticular, in ultrathin portable terminals in which the thickness ofthe thickest part of its housing is no greater than 21 mm, it is desiredthat the thickness of the liquid crystal display unit is about 4 mm to 5mm, and thus, even further a reduction in thickness of the edge-litbacklight unit incorporated into the liquid crystal display unit hasbeen desired.

In regard to the edge-lit backlight unit of such an ultrathin portableterminal, in addition to the edge-lit backlight unit having thereflection sheet 115 disposed on the back face of the optical waveguidesheet 111 shown in FIG. 7 a, an edge-lit backlight unit is also proposedin which a reduction in thickness is attempted, as shown in FIG. 7 b, byomitting the reflection sheet 115 shown in FIG. 7 a. The edge-litbacklight unit 210 shown in FIG. 7 b includes a metal top plate 216, anoptical waveguide sheet 211 overlaid on the front face of the top plate216, an optical sheet 212 overlaid on the front face of the opticalwaveguide sheet 211, and a light source 217 that emits rays of lighttoward the end face of the optical waveguide sheet 211. The front faceof the top plate 216 is finished by polishing and functions as areflection surface 216 a. In this example, the rays of light that havebeen emitted from the light source 217 and have entered the opticalwaveguide sheet 211 propagate through the optical waveguide sheet 211,and a part of the propagating rays of light exit from the back face ofthe optical waveguide sheet 211, are reflected on the reflection surface216 a as the front face of the top plate 216, and enter again theoptical waveguide sheet 211. Thus, in the edge-lit backlight unit 210shown in FIG. 7 b, the front face of the top plate 216 corresponds tothe reflection surface 216 a, and therefore the reflection surface 216 acan serve as a substitute for the reflection sheet 115 shown in FIG. 7a. Therefore, such an edge-lit backlight unit 210 omits the reflectionsheet 115, leading to a facilitation of the reduction in thickness. Inaddition, some edge-lit backlight units for such ultrathin portableterminals include an optical waveguide sheet (light guide film) havingan average thickness of no greater than 600 μm, whereby a furtherreduction in thickness is achieved.

PRIOR ART DOCUMENTS

Patent Document 1: Japanese Unexamined Patent Application, PublicationNo. 2010-177130

SUMMARY OF THE INVENTION

The present inventors found that when such a liquid crystal displaydevice is used, a drawback arises that luminance of the liquid crystaldisplay surface is uneven (lack in uniformity of luminance). The presentinventors thoroughly investigated the cause of the drawback, andconsequently found the back face of the optical waveguide sheet adheres(sticks) to the front face of the reflection sheet or the top platedisposed on the back face side of the optical waveguide sheet, and thenrays of light enter the adhering portion, leading to the lack inuniformity of luminance.

The present invention was made in view of the foregoing circumstances,and an object of the present invention is to provide an opticalwaveguide sheet in which, when used in an edge-lit backlight unit, thereduction in thickness thereof is achieved while inhibiting the lack inuniformity of luminance of a liquid crystal display surface. Moreover,another object of the present invention is to provide an edge-litbacklight unit and a portable terminal that achieve a reduction inthickness thereof while suppressing the lack in uniformity of luminance.

According to a first aspect of the present invention made for solvingthe aforementioned problems, an optical waveguide sheet for use in anedge-lit backlight unit, the optical waveguide sheet having a functionof allowing rays of light to enter the end face of the optical waveguidesheet and emitting the rays of light from the front face substantiallyuniformly, includes on the back side thereof: a sticking preventivemeans; and a plurality of recessed portions falling toward a front faceside, and the sticking preventive means includes: a plurality of annularraised portions each provided around each of the plurality of recessedportions and projecting toward the back face side; and a plurality ofprotruding portions provided scatteredly in a region which does notinclude the annular raised portions.

Since the optical waveguide sheet includes on the back face sidethereof, the plurality of recessed portions falling toward the frontface side, the optical waveguide sheet enables rays of light havingentered the recessed portions to be scattered toward the front faceside. Therefore, according to the optical waveguide sheet, providing theplurality of recessed portions in desired positions and scatteringincident light by means of the recessed portions enables the rays oflight to be emitted substantially uniformly from the front face side.Moreover, due to the optical waveguide sheet including as the stickingpreventive means: the plurality of annular raised portions each providedaround each of the plurality of recessed portions and projecting towardthe back face side; and the plurality of protruding portions providedscatteredly in a region which does not include the annular raisedportions, the optical waveguide sheet abuts the reflection sheet, thetop plate or the like disposed on the back face side of the opticalwaveguide sheet at dispersed points by way of the plurality of annularraised portions and the plurality of protruding portions, whereby theadhesion of the back face of the optical waveguide sheet to thereflection sheet, the top plate or the like can be inhibited. Therefore,the optical waveguide sheet can inhibit rays of light from entering suchan adhering portion to give rise to the lack in uniformity of luminance,and additionally it is not necessary to separately provide a stickingpreventive layer on the back face of the optical waveguide sheet,whereby the reduction in thickness can be facilitated. Furthermore, dueto the annular raised portions being provided around the recessedportions, the optical waveguide sheet can properly inhibit the adhesionat the recessed portions and in the vicinity of the recessed portions,and consequently the lack in uniformity of luminance due to the rays oflight scattered by the recessed portion can be favorably inhibited.

The optical waveguide sheet preferably is preferably for use as a lightguide film having an average thickness of no less than 100 μm and nogreater than 600 μm. Thus, the optical waveguide sheet can be suitablyused in a backlight unit for ultrathin portable terminals.

The average height (H₃) of the protruding portions from a back face onaverage level of the optical waveguide sheet (hereinafter, may be simplyreferred to as “back face on average level”) is preferably no less than2 μm and no greater than 7 μm. Thus, sticking to the reflection sheet,the top plate or the like disposed on the back face side can befavorably inhibited, and additionally the generation of scratches on thefront face of the reflection sheet or the top plate due to the abuttingthereof on the protruding portions can be inhibited.

The protruding portions have a height ratio (H₃/D₃) of the averageheight (H₃) to the average diameter (D₃) on the back face on averagelevel of preferably no less than 0.05 and no greater than 0.5. Thus,scratch-inhibiting ability with respect to the front face of thereflection sheet or the top plate disposed on the back face side andsticking-preventing ability can be improved.

The average height (H₂) of the annular raised portions from the backface on average level is preferably no less than 0.1 μm and no greaterthan 6 μm. Thus, the sticking-preventing ability of the recessedportions and the vicinity thereof can be improved, and additionally thelack in uniformity of luminance due to the rays of light scattered bythe recessed portions can be properly inhibited. Moreover, according tosuch a configuration, the generation of scratches on the front face ofthe reflection sheet or the top plate due to the abutting thereof on theannular raised portions can be inhibited.

The the annular raised portions have a height ratio (H₂/W₂) of theaverage height (H₂) to the average width (W₂) on the back face onaverage level of preferably no less than 0.04 and no greater than 0.8.Thus, the scratch-inhibiting ability with respect to the front face ofthe reflection sheet or the top plate disposed on the back face side andthe sticking-preventing ability can be improved.

It is preferred that an arrangement pattern of the protruding portionsis formed such that the arrangement density of the protruding portionson the back face gradually increases from a first end to a second end,and an arrangement pattern of the annular raised portions is formed suchthat the arrangement density of the annular raised portions on the backface gradually decreases from the first end to the second end. Thus,rays of light can be suitably scattered by the recessed portions, andconsequently in-plane uniformity of outgoing rays of light can beimproved. Moreover, according to such a configuration, it may befacilitated to suitably form the arrangement pattern of the protrudingportions in accordance with the arrangement pattern of the annularraised portions each provided around each of the recessed portions,whereby the sticking can be properly inhibited.

The optical waveguide sheet preferably contains a polycarbonate resin asa principal component. Thus, total reflection is likely to occur on thefront and back faces of the optical waveguide sheet and consequently therays of light are enabled to efficiently propagate, since thepolycarbonate resin has superior transparency and a high refractiveindex. In addition, since the polycarbonate resin has heat resistance,occurrence of deterioration due to heat generation from the lightsource, and the like may be minimized. Furthermore, the polycarbonateresin exhibits a more moderate water absorbing property as compared withacrylic resins and the like, leading to superior dimension accuracy.Therefore, due to containing the polycarbonate resin as a principalcomponent, degradation of the optical waveguide sheet over time can beinhibited.

According to a second aspect of the present invention made for solvingthe aforementioned problems, an edge-lit backlight unit includes theoptical waveguide sheet having the configuration described above, and alight source that emits rays of light toward the end face of the opticalwaveguide sheet.

Due to including the optical waveguide sheet according to the firstaspect of the present invention, the backlight unit can scatter the raysof light having entered the plurality of recessed portions provided onthe back face of the optical waveguide sheet toward the front face side.Therefore, providing the plurality of recessed portions at desiredpositions on the back face of the optical waveguide sheet, andscattering incident light by means of the recessed portions enables thebacklight unit to emit rays of light substantially uniformly from thefront face side. Moreover, according to the backlight unit, due to theoptical waveguide sheet including as the sticking preventive means: theplurality of annular raised portions each provided around each of theplurality of recessed portions and projecting toward the back face side;and the plurality of protruding portions provided scatteredly in aregion which does not include the annular raised portions, the opticalwaveguide sheet abuts the reflection sheet, the top plate or the likedisposed on the back face side of the optical waveguide sheet atdispersed points by way of the plurality of annular raised portions andthe plurality of protruding portions, whereby the adhesion of the backface of the optical waveguide sheet to the reflection sheet, the topplate or the like can be inhibited. Therefore, the backlight unit caninhibit rays of light from entering such an adhering portion to giverise to the lack in uniformity of luminance, and additionally it is notnecessary to separately provide a sticking preventive layer on the backface of the optical waveguide sheet, whereby the reduction in thicknesscan be facilitated. Furthermore, due to the annular raised portionsprovided on the back face of the optical waveguide sheet being providedaround the recessed portions, the backlight unit can properly inhibitthe adhesion at the recessed portions and in the vicinity of therecessed portions, and consequently the lack in uniformity of luminancedue to the rays of light scattered by the recessed portion can befavorably inhibited.

According to a third aspect of the present invention made for solvingthe aforementioned problems, a portable terminal includes the backlightunit having the configuration described above according to the secondaspect of the present invention in a liquid crystal display unit.

Due to including the backlight unit including the optical waveguidesheet according to the first aspect of the present invention, theportable terminal can emit rays of light substantially uniformly fromthe front face of the optical waveguide sheet, and additionally stickingof the optical waveguide sheet to the reflection sheet, the top plate orthe like disposed on the back face side of the optical waveguide sheetcan be inhibited. In addition, due to including the backlight unitincluding the optical waveguide sheet according to the first aspect ofthe present invention, the portable terminal can facilitate thereduction in thickness.

It is to be noted that the term “front face” of the optical waveguidesheet as referred to herein means a side toward which the opticalwaveguide sheet emits rays of light, and hence a display surface side ofa liquid crystal display unit. Moreover, the term “back face” of theoptical waveguide sheet as referred to means a face on the other side ofthe front face, and hence the other side of the display surface of theliquid crystal display unit. The term “average thickness” as referred tomeans an average of values determined in accordance with A-2 methodprescribed in JIS-K-7130, section 5.1.2. The term “diameter” as referredto means an intermediate value between the maximum diameter and themaximum length of the secant along a direction perpendicular to themaximum diameter direction. The “width” of the annular raised portion asreferred to means a difference between an outer radius and an innerradius of the annular raised portion.

As explained in the foregoing, when the optical waveguide sheetaccording to the first aspect of the present invention is used in anedge-lit backlight unit, the lack in uniformity of luminance of a liquidcrystal display surface can be inhibited and a reduction in thicknesscan be achieved. Therefore, the edge-lit backlight unit according to thesecond aspect of the present invention including the optical waveguidesheet according to the first aspect of the present invention, and theportable terminal according to the third aspect of the present inventionincluding the backlight unit enable inhibition of the lack in uniformityof luminance of a liquid crystal display unit, and a reduction inthickness to be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic perspective view of a portable terminalaccording to an embodiment of the present invention illustrating: (a) astate in which a liquid crystal display unit is lifted; and (b) a statein which the liquid crystal display unit is closed;

FIG. 2 shows a schematic cross sectional view illustrating an edge-litbacklight unit of the portable terminal shown in FIG. 1;

FIG. 3 shows a schematic rear view of an optical waveguide sheet of thebacklight unit shown in FIG. 2;

FIG. 4 shows a schematic enlarged view illustrating: (a) a crosssectional view; and (b) a rear view of a recessed portion and an annularraised portion of the optical waveguide sheet shown in FIG. 3;

FIG. 5 shows a schematic enlarged cross sectional view illustrating aprotruding portion of the optical waveguide sheet shown in FIG. 3;

FIG. 6 shows a schematic enlarged view illustrating the shape in aplanar view of an annular raised portion according to other embodimentof the present invention;

FIG. 7 shows a schematic cross sectional view illustrating aconventional edge-lit backlight unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred modes for carrying out the invention will beexplained in more detail with references to the drawings, if necessary.

First Embodiment Portable Terminal

A portable terminal 1 shown in FIG. 1 includes an operation unit 2, anda liquid crystal display unit 3 rotatably (enabling to be opened/closed)attached to the operation unit 2. A housing of the portable terminal 1(i.e., a casing that totally accommodates components of the portableterminal 1) has a thickness of no greater than 21 mm at the thickestpart when the liquid crystal display unit 3 is closed, and therefore theportable terminal 1 is an ultrathin laptop computer (hereinafter, may bealso referred to as “ultrathin computer 1”).

The liquid crystal display unit 3 of the ultrathin computer 1 includes aliquid crystal panel 4, and an edge-lit, ultrathin backlight unit thatemits rays of light toward the liquid crystal panel 4 from the back faceside. The liquid crystal panel 4 is held at the back face, the lateralface and a circumference of the front face by a casing for a liquidcrystal display unit 5 of the housing. In this embodiment, the casingfor a liquid crystal display unit 5 includes a top plate 6 disposed onthe back face (and the rear face) of the liquid crystal panel 4, and afront face support member 7 disposed on the front face side of thecircumference of the front face of the liquid crystal panel 4. Thehousing of the ultrathin computer 1 includes the casing for a liquidcrystal display unit 5, and a casing for an operation unit 9 that isrotatably attached to the casing for a liquid crystal display unit 5 viaa hinge part 8 and contains a central processing unit (ultra-low voltageCPU) and the like.

The average thickness of the liquid crystal display unit 3 is notparticularly limited as long as the housing thickness falls within adesired range, but the upper limit of the average thickness of theliquid crystal display unit 3 is preferably 7 mm, more preferably 6 mm,and still more preferably 5 mm. On the other hand, the lower limit ofthe average thickness of the liquid crystal display unit 3 is preferably2 mm, more preferably 3 mm, and still more preferably 4 mm. When theaverage thickness of the liquid crystal display unit 3 exceeds the upperlimit, it may be difficult to satisfy a requirement of a reduction inthickness of the ultrathin computer 1. On the other hand, when theaverage thickness of the liquid crystal display unit 3 is less than thelower limit, a decrease in strength and/or in luminance and the like ofthe liquid crystal display unit 3 may be incurred.

Backlight Unit

A backlight unit 11 shown in FIG. 2 is to be included in the liquidcrystal display unit 3 of the ultrathin computer 1. The backlight unit11 is configured as an edge-lit backlight unit that includes an opticalwaveguide sheet 12, a light source 13 that emits rays of light towardthe end face of the optical waveguide sheet 12, a reflection sheet 14disposed on the back face side of the optical waveguide sheet 12, and anoptical sheet 15 disposed on the front face side of the opticalwaveguide sheet 12.

Optical Waveguide Sheet

The optical waveguide sheet 12 allows the rays of light having enteredfrom the end face to exit from the front face substantially uniformly.The optical waveguide sheet 12 includes a sticking preventive means onthe back face thereof, as shown in FIG. 3. In addition, the opticalwaveguide sheet 12 includes on the back face side thereof, a pluralityof recessed portions 16 falling toward the front face side. The opticalwaveguide sheet 12 includes as the sticking preventive means: aplurality of annular raised portions 17 each provided around each of aplurality of recessed portions 16 and projecting toward the back faceside; and a plurality of protruding portions 18 provided scatteredly ina region which does not include the annular raised portions 17. Theoptical waveguide sheet 12 is formed into a plate (non-wedge shape) thatis substantially rectangular-shaped in a planar view and has asubstantially uniform thickness.

The upper limit of the average thickness of the optical waveguide sheet12 is preferably 600 μm, more preferably 580 μm, and still morepreferably 550 μm. On the other hand, the lower limit of the averagethickness of optical waveguide sheet 12 is preferably 100 μm, morepreferably 150 μm, and still more preferably 200 μm. When the averagethickness of the optical waveguide sheet 12 exceeds the upper limit, itmay be difficult to use the optical waveguide sheet 12 as a thin lightguide film desired for the ultrathin portable terminals, andconsequently it may be difficult to satisfy a requirement of a reductionin thickness of the backlight unit 11. To the contrary, when the averagethickness of the optical waveguide sheet 12 is less than the lowerlimit, the strength of the optical waveguide sheet 12 may beinsufficient, and a sufficient amount of rays of light from the lightsource 13 may not be introduced to the optical waveguide sheet 12.

The lower limit of the required light guide distance of the opticalwaveguide sheet 12 from the end face thereof on the light source 13 sideis preferably 7 cm, more preferably 9 cm, and still more preferably 11cm. On the other hand, the upper limit of the required light guidedistance of the optical waveguide sheet 12 from the end face thereof onthe light source 13 side is preferably 45 cm, more preferably 43 cm, andstill more preferably 41 cm. When the required light guide distance isless than the lower limit, the optical waveguide sheet 12 may not beused in larger size terminals other than small-size portable terminals.To the contrary, when the required light guide distance exceeds theupper limit, bending is likely to occur in the use of the opticalwaveguide sheet 12 as a thin light guide film having an averagethickness of no greater than 600 μm, and additionally sufficient lightguiding properties may not be achieved. It is to be noted that therequired light guide distance of the optical waveguide sheet 12 from theend face thereof on the light source 13 side as referred to means adistance which the rays of light emitted from the light source 13 andentering the end face of the optical waveguide sheet 12 need to travelfrom the end face toward the opposed end face. Specifically, forexample, for unilateral edge-lit backlight units, the required lightguide distance of the optical waveguide sheet 12 from the end facethereof on the light source 13 side means a distance from the end faceof the optical waveguide sheet on the light source side to the opposedend face, and for bilateral edge-lit backlight units, the required lightguide distance is a distance from the end face of the optical waveguidesheet on the light source side to the central portion.

The lower limit of the surface area of the optical waveguide sheet 12 ispreferably 150 cm², more preferably 180 cm², and still more preferably200 cm². On the other hand, the upper limit of the surface area of theoptical waveguide sheet 12 is preferably 1,000 cm², more preferably 950cm², and still more preferably 900 cm². When the surface area of theoptical waveguide sheet 12 is less than the lower limit, the opticalwaveguide sheet 12 may not be used in larger size terminals other thansmall-size portable terminals. To the contrary, when the surface area ofthe optical waveguide sheet 12 exceeds the upper limit, bending islikely to occur in the use of the optical waveguide sheet 12 as a thinlight guide film having an average thickness of no greater than 600 μm,and additionally sufficient light guiding properties may not beachieved.

Since the optical waveguide sheet 12 needs to transmit rays of light,the optical waveguide sheet 12 is formed from a transparent, inparticular colorless and transparent synthetic resin as a principalcomponent. The principal component of the optical waveguide sheet 12 isexemplified by a polycarbonate resin, an acrylic resin, polyethyleneterephthalate, polyethylene naphthalate, polystyrene, amethyl(meth)acrylate-styrene copolymer, polyolefin, a cycloolefinpolymer, a cycloolefin copolymer, cellulose acetate, weather resistantvinyl chloride, an active energy ray-curable resin, and the like. Of thetransparent synthetic resins, a polycarbonate resin or an acrylic resinis preferred as the principal component of the optical waveguide sheet12. Since the polycarbonate resin has superior transparency and a highrefractive index, when the optical waveguide sheet 12 contains thepolycarbonate resin as a principal component, total reflection is likelyto occur on the front and back faces of the optical waveguide sheet 12,whereby the rays of light can be efficiently propagated. Moreover, sincethe polycarbonate resin has heat resistance, deterioration thereof dueto heat generation of the light source 13, and the like is less likelyto occur. Furthermore, the polycarbonate resin has a more moderate waterabsorbing property as compared with acrylic resins and the like, andaccordingly is superior in dimension accuracy. Therefore, when theoptical waveguide sheet 12 contains the polycarbonate resin as aprincipal component, degradation thereof over time can be inhibited. Onthe other hand, since the acrylic resins have a higher degree oftransparency, a loss of rays of light in the optical waveguide sheet 12can be minimized. The optical waveguide sheet 12 contains the principalcomponent in a proportion of preferably no less than 80% by mass, morepreferably no less than 90% by mass, and still more preferably no lessthan 98%.

The polycarbonate resin is not particularly limited, and may be any oneof a linear polycarbonate resin and a branched polycarbonate resin, ormay be a polycarbonate resin mixture that contains both of the linearpolycarbonate resin and the branched polycarbonate resin.

The linear polycarbonate resin is exemplified by a linear aromaticpolycarbonate resin produced by a well-known phosgene process or a meltprocess, and the linear aromatic polycarbonate resin is constituted witha carbonate component and a diphenol component. Examples of a precursorfor introducing the carbonate component include phosgene, diphenylcarbonate, and the like. Moreover, examples of the diphenol include2,2-bis(4-hydroxyphenyl)propane,2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,1,1-bis(4-hydroxyphenyl)cyclohexane,1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane,1,1-bis(4-hydroxyphenyl)decane, 1,1-bis(4-hydroxyphenyl)cyclodecane,1,1-bis(4-hydroxyphenyl)propane,1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclododecane,4,4′-dihydroxydiphenyl ether, 4,4′-thiodiphenol,4,4′-dihydroxy-3,3-dichlorodiphenyl ether, and the like. These may beused either alone or in combination of two or more types thereof.

The branched polycarbonate resin is exemplified by a polycarbonate resinproduced using a branching agent, and examples of the branching agentinclude phloroglucin, trimellitic acid,1,1,1-tris(4-hydroxyphenyl)ethane, 1,1,2-tris(4-hydroxyphenyl)ethane,1,1,2-tris(4-hydroxyphenyl)propane, 1,1,1-tris(4-hydroxyphenyl)methane,1,1,1-tris(4-hydroxyphenyl)propane,1,1,1-tris(2-methyl-4-hydroxyphenyl)methane,1,1,1-tris(2-methyl-4-hydroxyphenyl)ethane,1,1,1-tris(3-methyl-4-hydroxyphenyl)methane,1,1,1-tris(3-methyl-4-hydroxyphenyl)ethane,1,1,1-tris(3,5-dimethyl-4-hydroxyphenyl)methane,1,1,1-tris(3,5-dimethyl-4-hydroxyphenyl)ethane,1,1,1-tris(3-chloro-4-hydroxyphenyl)methane,1,1,1-tris(3-chloro-4-hydroxyphenyl)ethane,1,1,1-tris(3,5-dichloro-4-hydroxyphenyl)methane,1,1,1-tris(3,5-dichloro-4-hydroxyphenyl)ethane,1,1,1-tris(3-bromo-4-hydroxyphenyl)methane,1,1,1-tris(3-bromo-4-hydroxyphenyl)ethane,1,1,1-tris(3,5-dibromo-4-hydroxyphenyl)methane,1,1,1-tris(3,5-dibromo-4-hydroxyphenyl)ethane,4,4′-dihydroxy-2,5-dihydroxydiphenyl ether, and the like.

The acrylic resin is exemplified by a resin having a skeleton derivedfrom acrylic acid or methacrylic acid. Although the acrylic resin is notparticularly limited, examples thereof include: poly(meth)acrylic acidesters such as polymethyl methacrylate; methylmethacrylate-(meth)acrylic acid copolymers; methylmethacrylate-(meth)acrylic acid ester copolymers; methylmethacrylate-acrylic acid ester-(meth)acrylic acid copolymers;methyl(meth)acrylate-styrene copolymers; polymers having an alicyclichydrocarbon group (for example, methyl methacrylate-cyclohexylmethacrylate copolymers, methyl methacrylate-norbornyl(meth)acrylatecopolymers); and the like. Of these acrylic resins, poly(meth)acrylicacid C1-6 alkyl esters such as polymethyl(meth)acrylate are preferred,and methyl methacrylate resins are more preferred.

Examples of the active energy ray-curable resin include active energyray curable acrylic resins, active energy ray-curable epoxy resins, andthe like. The active energy ray-curable resin may be used, for example,in the form of a resin containing at least one of a photopolymerizableprepolymer, a photopolymerizable oligomer and a photopolymerizablemonomer, as well as a photopolymerization initiator or the like.

Examples of the prepolymer and the oligomer which may be contained inthe active energy ray-curable acrylic resin includeepoxy(meth)acrylates, urethane (meth)acrylates,polyester(meth)acrylates, poly ether(meth)acrylates, and the like.

In addition, examples of the monomer which may be contained in theactive energy ray-curable acrylic resin include:monofunctional(meth)acrylates such as methyl(meth)acrylate,lauryl(meth)acrylate, ethoxy diethylene glycol(meth)acrylate, methoxytriethylene glycol(meth)acrylate, phenoxyethyl(meth)acrylate,tetrahydrofurfuryl(meth)acrylate, isobornyl(meth)acrylate,2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate and2-hydroxy-3-phenoxy(meth)acrylate; polyfunctional(meth)acrylates such asneopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, dipentaerythritoltri(meth)acrylate, dipentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, tripentaerythritol tri(meth)acrylate,tripentaerythritol hexa(meth)triacrylate, trimethylolpropanebenzoate(meth)acrylate and trimethylolpropane benzoate; urethaneacrylates such as glycerin di(meth)acrylate, hexamethylene diisocyanateand pentaerythritol tri(meth)acrylate hexamethylene diisocyanate; andthe like.

Examples of the photopolymerization initiator include: carbonylcompounds such as acetophenone, 2,2-diethoxyacetophenone,p-dimethylacetophenone, p-dimethylaminopropiophenone, benzophenone,benzil, 2-chlorobenzophenone, 4,4′-dichlorobenzophenone,4,4′-bisdiethylaminobenzophenone, Michler ketone, benzoin, benzoinmethyl ether, benzoin ethyl ether, benzoin isopropyl ether, methylbenzoylformate, p-isopropyl-α-hydroxyisobutylphenone,α-hydroxyisobutylphenone, 2,2-dimethoxy-2-phenylacetophenone and1-hydroxycyclohexyl phenyl ketone; sulfur compounds such astetramethylthiram monosulfide, tetramethylthiram disulfide, thiaxanthon,2-chlorothiaxanthon and 2-methylthiaxanthon; and the like. Thesephotopolymerization initiators may be used either alone, or incombination of two or more types thereof.

It is to be noted that the optical waveguide sheet 12 may contain anoptional component such as an ultraviolet ray-absorbing agent, a fireretardant, a stabilizer, a lubricant, a processing aid, a plasticizer,an impact resistant aid, a retardation reducing agent, a delusteringagent, an antimicrobial, a fungicide, an antioxidant, a release agentand an antistatic agent.

The recessed portion 16 is configured as a light scattering portion forscattering incident light toward the front face side. The recessedportion 16 is formed to be substantially circular in a planar view, asshown in FIGS. 3 and 4. In addition, the recessed portion 16 is formedsuch that the diameter thereof gradually decreases toward the front faceside. The three-dimensional shape of the recessed portion 16 is notparticularly limited, and may be hemispherical, substantiallyhemispherical, conical, frustoconical, cylindrical, or the like. Ofthese, the three-dimensional shape of the recessed portion 16 ispreferably hemispherical. When the three-dimensional shape of therecessed portion 16 is hemispherical, the moldability of the recessedportion 16 can be improved, and additionally the rays of light havingentered the recessed portion 16 can be suitably scattered. Thearrangement pattern of the recessed portions 16 is formed such that thearrangement density thereof on the back face gradually decreases from afirst end to a second end. In particular, the arrangement pattern of therecessed portions 16 is formed such that the arrangement density thereofon the back face gradually decreases from the edge on the side oppositeto the light source 13 to the edge on the light source 13 side.

The upper limit of the average depth (L₁) of the recessed portions 16from the back face on average level is preferably 10 μm, more preferably9 μm, and still more preferably 7 μm. On the other hand, the lower limitof the average depth (L₁) of the recessed portions 16 from the back faceon average level is preferably 1 μm, more preferably 2 μm, and stillmore preferably 4 μm. When the average depth (L₁) of the recessedportions 16 from the back face on average level exceeds the upper limit,the lack in uniformity of luminance may be brought about, andadditionally it may be difficult to satisfy a requirement of a reductionin thickness of the optical waveguide sheet 12. To the contrary, whenthe average depth (L₁) of the recessed portions 16 from the back face onaverage level is less than the lower limit, sufficient light scatteringeffects may not be achieved.

The upper limit of the average diameter (D₁) of the recessed portions 16on the back face on average level is preferably 50 μm, more preferably40 μm, and still more preferably 30 μm. On the other hand, the lowerlimit of the average diameter (D₁) of the recessed portions 16 on theback face on average level is preferably 10 μm, more preferably 12 μm,and still more preferably 15 μm. When the average diameter (D₁) of therecessed portions 16 on the back face on average level exceeds the upperlimit, the lack in uniformity of luminance may be brought about. To thecontrary, when the average diameter (D₁) of the recessed portions 16 onthe back face on average level is less than the lower limit, sufficientlight scattering effects may not be achieved.

The annular raised portions 17 are integrally formed on the back face ofthe optical waveguide sheet 12. The annular raised portion 17 projectstoward the back face side such that the annular raised portion 17extends beyond the lower end of the recessed portion 16. The annularraised portion 17 is formed so as to surround the recessed portion 16annularly in a planar view, as shown in FIGS. 3 and 4. The shape of theannular raised portion 17 in a planar view may be selected in accordancewith, for example, the shape of the outer periphery of the recessedportion 16, and may be annular, polygonal circular, or the like.Moreover, with respect to the shape of the annular raised portion 17 ina planar view, the annular raised portion 17 may not necessarilysurround the outer periphery of the recessed portion 16 completely, andmay partially surround the outer periphery of the recessed portion 16 asshown in FIG. 6, for example. Of these, an annular shape is preferred asthe shape of the annular raised portion 17 in a planar view. In theoptical waveguide sheet 12, when the annular raised portion 17 is formedto be annular, adhesion of the recessed portion 16 and the vicinitythereof to the reflection sheet 14 or the like disposed on the back faceside can be properly inhibited, whereby the lack in uniformity ofluminance due to the rays of light scattered by the recessed portion 16can be favorably inhibited. In addition, the annular raised portion 17is shaped to have a rounded top. In the optical waveguide sheet 12,since the top of the annular raised portion 17 is rounded, thescratch-inhibiting ability with respect to the reflection sheet 14 orthe like disposed on the back face side can be enhanced.

The annular raised portion 17 is preferably formed so as to becontinuous with the recessed portion 16. Specifically, it is preferredthat the inner periphery of the annular raised portion 17 substantiallyconforms to the periphery of the recessed portion 16. Moreover, it ispreferred that the internal surface of the annular raised portion 17 issmoothly and continuously joined to the inner face of the recessedportion 16. When the annular raised portion 17 is smoothly andcontinuously joined to the recessed portion 16, the lack in uniformityof luminance of the rays of light scattered by the recessed portion 16and exiting from the front face of the optical waveguide sheet 12 can beproperly inhibited. The term “periphery” as referred to herein means acurve given by the intersection of the three-dimensional shape (recessedportion 16 or annular raised portion 17) with the average level of theback face of the optical waveguide sheet 12. Moreover, the term “innerperiphery” as referred to means the periphery of the internal surface ofthe annular raised portion 17.

The arrangement pattern of the annular raised portions 17 is formed suchthat the arrangement density thereof on the back face graduallydecreases from a first end to a second end. In particular, thearrangement pattern of the annular raised portions 17 is formed suchthat the arrangement density thereof on the back face graduallydecreases from the edge on the side opposite to the light source 13 tothe edge on the light source 13 side.

The upper limit of the average height (H₂) of the annular raisedportions 17 from the back face on average level is preferably 6 μm, morepreferably 5 μm, and still more preferably 4 μm. On the other hand, thelower limit of the average height (H₂) of the annular raised portions 17from the back face on average level is preferably 0.1 μm, morepreferably 0.3 μm, and still more preferably 0.6 μm. When the averageheight (H₂) of the annular raised portions 17 from the back face onaverage level exceeds the upper limit, scratches may be generated on thefront face of the reflection sheet 14 or the like disposed on the backface side due to the abutting thereof on the annular raised portion 17.To the contrary, when the average height (H₂) of the annular raisedportions 17 from the back face on average level is less than the lowerlimit, the sticking may not be properly inhibited. Whereas, when theaverage height (H₂) of the annular raised portions 17 from the back faceon average level falls within the range described above, thescratch-inhibiting ability of the reflection sheet 14 or the likedisposed on the back face side and the sticking-preventing ability maybe improved, and in particular, the lack in uniformity of luminance dueto the rays of light scattered by the recessed portion 16 can beproperly inhibited.

The upper limit of the average width (W₂) of the annular raised portions17 on the back face on average level is preferably 15 μm, morepreferably 12 μm, and still more preferably 10 μm. On the other hand,the lower limit of the average width (W₂) of the annular raised portions17 on the back face on average level is preferably 1 μm, more preferably3 μm, and still more preferably 5 μm. When the average width (W₂) of theannular raised portions 17 on the back face on average level exceeds theupper limit, an area in which the annular raised portion 17 is incontact with the reflection sheet 14 or the like may be increased, andconsequently the lack in uniformity of luminance may be brought about.To the contrary, when the average width (W₂) of the annular raisedportions 17 on the back face on average level is less than the lowerlimit, scratches may be generated on the front face of the reflectionsheet 14 or the like disposed on the back face side due to the abuttingthereof on the annular raised portion 17.

The upper limit of the height ratio (H₂/W₂) of the average height (H₂)from the back face on average level to the average width (W₂) on theback face on average level in the annular raised portions 17 ispreferably 0.8, more preferably 0.6, and still more preferably 0.4. Onthe other hand, the lower limit of the height ratio (H₂/W₂) of theaverage height (H₂) from the back face on average level to the averagewidth (W₂) on the back face on average level in the annular raisedportions 17 is preferably 0.04, more preferably 0.06, and still morepreferably 0.08. When the height ratio (H₂/W₂) exceeds the upper limit,scratches may be generated on the front face of the reflection sheet 14or the like disposed on the back face side. To the contrary, when theheight ratio (H₂/W₂) is less than the lower limit, the sticking may notbe properly inhibited.

The upper limit of the width ratio (W₂/D₁) of the average width (W₂) ofthe annular raised portions 17 to the average diameter (D₁) of therecessed portions 16 is preferably 1, more preferably 0.8, and stillmore preferably 0.6. On the other hand, the lower limit of the widthratio (W₂/D₁) of the average width (W₂) of the annular raised portions17 to the average diameter (D₁) of the recessed portions 16 ispreferably 0.1, more preferably 0.2, and still more preferably 0.3. Whenthe width ratio (W₂/D₁) exceeds the upper limit, an area in which theannular raised portion 17 is in contact with the reflection sheet 14 orthe like may be increased, and consequently the lack in uniformity ofluminance may be brought about. To the contrary, when the width ratio(W₂/D₁) is less than the lower limit, sufficient sticking-preventingeffects may not be achieved.

The protruding portions 18 are integrally formed on the back face of theoptical waveguide sheet 12. The protruding portion 18 is formed to besubstantially circular in a planar view. Moreover, the protrudingportion 18 is shaped to have a rounded top, as shown in FIG. 5. Thethree-dimensional shape of the protruding portion 18 is not particularlylimited, but is preferably hemispherical. When the three-dimensionalshape of the protruding portion 18 is hemispherical, the moldability ofprotruding portion 18 can be improved, and additionally thescratch-inhibiting ability with respect to the reflection sheet 14 orthe like disposed on the back face side can be improved. The arrangementpattern of the protruding portions 18 is formed such that thearrangement density thereof on the back face gradually increases from afirst end to a second end. In particular, the arrangement pattern of theprotruding portions 18 is formed such that the arrangement densitythereof on the back face gradually increases from the edge on the sideopposite to the light source 13 to the edge on the light source 13 side.

The upper limit of the average height (H₃) of the protruding portions 18from the back face on average level is preferably 7 μm, more preferably6 μm, and still more preferably 5 μm. On the other hand, the lower limitof the average height (H₃) of the protruding portions 18 from the backface on average level is preferably 2 μm, more preferably 3 μm, andstill more preferably 4 μm. When the average height (H₃) of theprotruding portions 18 from the back face on average level exceeds theupper limit, scratches may be generated on the front face of thereflection sheet 14 or the like disposed on the back face side due tothe abutting thereof on the protruding portion 18. To the contrary, whenthe average height (H₃) of the protruding portions 18 from the back faceon average level is less than the lower limit, the sticking may not beproperly inhibited.

The upper limit of the height ratio (H₃/D₃) of the average height (H₃)to the average diameter (D₃) on the back face on average level in theprotruding portions 18 is preferably 0.5, more preferably 0.3, and stillmore preferably 0.2. On the other hand, the lower limit of the heightratio (H₃/D₃) of the average height (H₃) to the average diameter (D₃) onthe back face on average level in the protruding portions 18 ispreferably 0.05, more preferably 0.07, and still more preferably 0.1.When the height ratio (H₃/D₃) exceeds the upper limit, scratches may begenerated on the front face of the reflection sheet 14 or the likedisposed on the back face side. To the contrary, when the height ratio(H₃/D₃) is less than the lower limit, the sticking may not be properlyinhibited.

The upper limit of the height ratio (H₃/H₂) of the average height (H₃)of the protruding portions 18 to the average height (H₂) of the annularraised portions 17 is preferably 7, more preferably 5, and still morepreferably 3. On the other hand, the lower limit of the height ratio(H₃/H₂) of the average height (H₃) of the protruding portions 18 to theaverage height (H₂) of the annular raised portions 17 is preferably ½,more preferably ⅔, and still more preferably 1. When the height ratio(H₃/H₂) does not fall within the range, the difference between theaverage height (H₃) of the protruding portions 18 and the average height(H₂) of the annular raised portions 17 is so significant that overallsticking-preventing ability may not be sufficiently exhibited. Whereas,when the height ratio (H₃/H₂) falls within the range described above,the overall sticking-preventing ability may be improved, andadditionally the lack in uniformity of luminance can be effectivelyinhibited due particularly to an improvement of the sticking-preventingability of the recessed portion 16 and the vicinity thereof.

The upper limit of the total arrangement density of the annular raisedportions 17 and the protruding portions 18 on the back face of theoptical waveguide sheet 12 is preferably 500 per mm², more preferably400 per mm², and still more preferably 300 per mm². On the other hand,the lower limit of the total arrangement density of the annular raisedportions 17 and the protruding portions 18 on the back face of theoptical waveguide sheet 12 is preferably 40 per mm², more preferably 60per mm², and still more preferably 80 per mm². When the totalarrangement density of the annular raised portions 17 and the protrudingportions 18 on the back face of the optical waveguide sheet 12 exceedsthe upper limit, scratches are highly likely to be generated on thefront face of the reflection sheet 14 or the like disposed on the backface side. To the contrary, when the total arrangement density of theannular raised portions 17 and the protruding portions 18 on the backface of the optical waveguide sheet 12 is less than the lower limit, thesticking-preventing ability may not be sufficiently exhibited. It is tobe noted that the total arrangement density of the annular raisedportions 17 and the protruding portions 18 is determined by counting thenumber of the annular raised portions 17 and the protruding portions 18found within a field of view observed using a laser microscope at amagnification of 1,000×, followed by the calculation based on the numberand the area of the field of view. Furthermore, in a case where aplurality of annular raised portions 17 surround a single recessedportion 16, the annular raised portions 17 as a whole are counted asbeing 1.

Reflection Sheet

The reflection sheet 14 is disposed on the back face side of the opticalwaveguide sheet 12, such that it abuts the plurality of annular raisedportions 17 and the plurality of protruding portions 18 each provided onthe back face of the optical waveguide sheet 12. The reflection sheet 14reflects the rays of light emitted from the back face side of theoptical waveguide sheet 12 toward the front face side. The reflectionsheet 14 is exemplified by: a white sheet in which a filler is containedin a dispersion state in a base resin such as polyester resin; a mirrorsheet obtained by vapor deposition of a metal such as aluminum andsilver on the surface of a film formed from a polyester resin or thelike to enhance regular reflection properties; and the like.

Light Source

The light source 13 is disposed such that an emission surface faces to(or abuts) the end face of the optical waveguide sheet 12. Various typesof light sources can be used as the light source 13, and for example, alight emitting diode (LED) can be used as the light source 13.Specifically, a light source in which a plurality of light emittingdiodes are arranged along the end face of the optical waveguide sheet 12may be used as the light source 13.

Optical Sheet

The optical sheet 15 has optical functions such as the diffusion andrefraction of rays of light having entered from the back face side. Theoptical sheet 15 is exemplified by: a light diffusion sheet having alight diffusion function; a prism sheet having a function of refractionin a normal direction; and the like.

Production Method of Optical Waveguide Sheet

The method for producing the optical waveguide sheet 12 is exemplifiedby:

(a) an injection molding process involving injecting a material forforming an optical waveguide sheet in a molten state into a mold havinga reversal shape of the plurality of recessed portions, the plurality ofannular raised portions each provided around each of the plurality ofrecessed portions, and the plurality of protruding portions providedscatteredly in a region which does not include the annular raisedportions;

(b) a method that involves heating again a sheet element constitutedfrom a material for forming an optical waveguide sheet, and pressing thesheet element between the mold having the reversal shape and a metalplate or a roller to transfer the shape thereof;

(c) a method which employs extrusion molding involving feeding amaterial for forming an optical waveguide sheet in a molten state to aT-die, extruding the forming material from an extruder and the T-die tomold a sheet element, and pressing the sheet element between the moldhaving the reversal shape and a metal plate or a roller to transfer theshape thereof;

(d) a casting process (solution casting process) that involvesdissolving a material for forming an optical waveguide sheet in asolvent to prepare a solution (dope) having a fluidity, pouring thesolution into the mold having the reversal shape, and evaporating thesolvent;

(e) a method that involves filling the mold having the reversal shapewith an uncured active energy ray-curable resin, and irradiating theuncured active energy ray-curable resin with an active energy ray suchas an ultraviolet ray;

(f) a method that involves providing the plurality of recessed portionsand the plurality of annular raised portion on one of the faces of asheet element in a similar manner to any one of the above alternatives(a) to (e) using a mold having merely a reversal shape of the pluralityof recessed portions and the plurality of annular raised portions eachprovided around each of the plurality of recessed portions, andproviding the plurality of protruding portions in a region which doesnot include the plurality of annular raised portions on one of the facesof the sheet element by way of a well-known printing process such asscreen printing and ink jet printing;

(g) a method that involves providing the plurality of recessed portionsand the plurality of annular raised portions on one of the faces of thesheet element in a similar manner to any one of the above alternatives(a) to (e) using a mold having merely a reversal shape of the pluralityof recessed portions and the plurality of annular raised portions eachprovided around each of the plurality of recessed portions, andproviding the plurality of protruding portions in a region which doesnot include the plurality of annular raised portions on one of the facesof the sheet element, by way of a photolithography process and anetching process;

(h) a method that involves providing the plurality of recessed portionsand the plurality of annular raised portions each provided around eachof the plurality of recessed portions on one of the faces of the sheetelement constituted from a material for forming an optical waveguidesheet by way of cutting with a carbide tool, a diamond tool, an end millor the like, and then providing the plurality of protruding portionsscatteredly in a region which does not include the plurality of annularraised portions on one of the faces of the sheet element using thewell-known printing process, or the photolithography process and theetching process; and the like.

Mold

The mold which may be used is exemplified by, as described above:

(i) a mold having, on the surface thereof, a reversal shape of theplurality of recessed portions 16 provided in a certain pattern, theplurality of annular raised portions 17 each provided around each of therecessed portion 16 and the plurality of protruding portions 18 providedscatteredly in a region which does not include the annular raisedportion 17; or

(ii) a mold having, on the surface thereof, merely a reversal shape ofthe plurality of recessed portions 16 provided in a certain pattern, andthe plurality of annular raised portions 17 each provided around each ofthe recessed portion 16.

Although the material for forming the mold is not particularly limited,examples thereof include metals such as nickel, gold, silver, copper andaluminum.

Production Method of Master Mold

The mold may be produced using a master mold having, on the surfacethereof, a plurality of recessed portions provided in a certain patternand a plurality of annular raised portions each provided around each ofthe plurality of recessed portions.

The production method of the master mold is exemplified by:

(A) a method in which the surface of a substrate for forming a mastermold is subjected to laser irradiation to simultaneously form theplurality of recessed portions and the plurality of annular raisedportions; and

(B) a method in which the surface of a substrate for forming a mastermold is cut out with a carbide tool, a diamond tool, an end mill or thelike to simultaneously form the plurality of recessed portions and theplurality of annular raised portions.

A material for forming the master mold produced according to the method(A) is exemplified by metals such as SUSs. On the other hand, a materialfor forming the master mold produced according to the method (B) isexemplified by metals such as SUSs, as well as comparatively rigidsynthetic resins such as polycarbonate resins and acrylic resins.

It is to be noted that when the laser irradiation is executed,laser-irradiated sites are melted. As a result, upon the formation ofthe recessed portions, the molten material is deposited around therecessed portion to form the annular raised portion. On the other hand,when the cutting is executed, the materials cut out from the substrateare deposited around the recessed portion formed in the cutting to formthe annular raised portion. The depth and/or the diameter of therecessed portion, as well as the height, width, shape and the like ofthe annular raised portion are adjusted by the laser irradiation or acutting intensity, an angle, a diameter, and the like.

Moreover, the laser which may be used in irradiation for the purpose offorming the plurality of recessed portions and the plurality of annularraised portions on the surface of the master mold is not particularlylimited, and examples thereof include a carbon dioxide laser, a carbonmonoxide laser, a semiconductor laser, a YAG (yttrium-aluminum-garnet)laser, and the like. Of these, a carbon dioxide laser is suitable forforming a minute shape, since the carbon monoxide laser produces beamshaving a wavelength of 9.3 to 10.6 μm. The carbon dioxide laser isexemplified by a transversely excited atmospheric pressure (TEA) carbondioxide laser, a continuous oscillation carbon dioxide laser, arepetitively pulsed carbon dioxide laser, and the like.

Production Method of Mold

The production method of the mold described in (ii) of the “Mold”section includes the steps of: (S1) providing by electroforming on thesurface of a master mold, a plating layer including a reversal shape ofthe master mold on the surface thereof, the master mold including theplurality of recessed portions provided in a certain pattern and theplurality of annular raised portions each provided around each of theplurality of recessed portions; and (S2) releasing the plating layerfrom the master mold. The production method of the mold described in (i)of the “Mold” section further includes the step of (S3) forming areversal shape of the plurality of protruding portions providedscatteredly in a region which does not include the plurality of annularraised portions on the surface of the plating layer released from themaster mold.

The plating layer-forming step (S1) is executed, for example, byapplying an electric current through nickel metal as an anode and themaster mold as a cathode in a plating bath, and thereby depositing aplating layer on the surface of the master mold.

The plating layer-releasing step (S2) is executed by releasing from themaster mold the plating layer deposited on the surface of the mastermold in the plating layer-forming step (S1). It is to be noted that theplating layer-releasing step (S2) may further include the step ofreinforcing the plating layer with a reinforcing member in order toincrease the strength of the plating layer released from the mastermold.

The step of forming a reversal shape of the protruding portions (S3) isexecuted by providing a reversal shape of the plurality of protrudingportions in a region not including the plurality of annular raisedportions on the surface of the plating layer formed in the platinglayer-releasing step (S2), by way of laser irradiation or cutting with acarbide tool, a diamond tool, an end mill or the like. According to thereversal shape of the plurality of protruding portions being formed onthe surface of the plating layer in the step of forming a reversal shapeof the protruding portions (S3), the plating layer is formed as themold. It is to be noted that a mold-releasing treatment layer may beprovided on the surface of the mold. The method for forming such amold-releasing treatment layer is exemplified by a method that involvesexecuting vapor deposition of titanium nitride (TiN) on the surface ofthe mold by sputtering to provide a coating film. Due to the mold havinga mold-releasing treatment layer on the surface thereof, adhesion of theresin sheet material to the mold can be inhibited.

Advantages

Since the optical waveguide sheet 12 includes on the back face sidethereof, the plurality of recessed portions 16 falling toward the frontface side, the optical waveguide sheet 12 enables the rays of lighthaving entered the recessed portions 16 to be scattered toward the frontface side. Therefore, the optical waveguide sheet 12 can emit rays oflight substantially uniformly from the front face side through formingthe plurality of recessed portions 16 in desired positions andscattering incident light by the recessed portions 16. In addition,since the optical waveguide sheet 12 includes as the sticking preventivemeans: the plurality of annular raised portions 17 each provided aroundeach of the plurality of recessed portions 16 and projecting toward theback face side; and the plurality of protruding portions 18 providedscatteredly in a region which does not include the annular raisedportions 17, the optical waveguide sheet 12 abuts the reflection sheet14 or the like disposed on the back face side of the optical waveguidesheet 12 at dispersed points by way of the plurality of annular raisedportions 17 and the plurality of protruding portions 18, wherebyadhesion of the back face of the optical waveguide sheet 12 to thereflection sheet 14 or the like can be inhibited. Therefore, the opticalwaveguide sheet 12 can inhibit rays of light from entering such anadhering portion to give rise to the lack in uniformity of luminance,and additionally it is not necessary to separately provide a stickingpreventive layer on the back face of the optical waveguide sheet,whereby the reduction in thickness can be facilitated. Furthermore,according to the optical waveguide sheet 12, since the adhesion of therecessed portions 16 and the vicinity thereof can be properly inhibiteddue to the annular raised portions 17 being provided around the recessedportions 16, the lack in uniformity of luminance due to the rays oflight scattered by the recessed portion 16 can be favorably inhibited.

According to the optical waveguide sheet 12, the arrangement pattern ofthe protruding portions 18 is formed such that the arrangement densitythereof on the back face gradually increases from a first end to asecond end, and the arrangement pattern of the annular raised portions17 is formed such that the arrangement density thereof on the back facegradually decreases from the first end to the second end; therefore,rays of light can be suitably scattered by the recessed portion 16, andconsequently the in-plane uniformity of outgoing rays of light can beimproved, and additionally it may be facilitated to suitably form thearrangement pattern of the protruding portions 18 in accordance with thearrangement pattern of the annular raised portions 17 each disposedaround each of the recessed portions 16, whereby the sticking can beproperly inhibited. In addition, according to the optical waveguidesheet 12, in particular, the arrangement pattern of recessed portions 16and the annular raised portions 17 is formed such that the arrangementdensity thereof on the back face gradually decreases from the edge onthe side opposite to the light source 13 to the edge on the light source13 side, the rate of light scattering in the vicinity of the lightsource 13 can be decreased, and the rate of light scattering can beincreased with an increase of the distance from the light source 13.Additionally, the lack in uniformity of luminance due to scattered raysof light can be properly inhibited. Accordingly, the in-plane uniformityof outgoing rays of light can be effectively enhanced.

Due to including the optical waveguide sheet 12, the backlight unit 11enables the rays of light having entered the plurality of recessedportions 16 provided on the back face of the optical waveguide sheet 12to be scattered toward the front face side. Therefore, the backlightunit 11 can emit rays of light substantially uniformly from the frontface side through forming the plurality of recessed portions 16 indesired positions on the back face of the optical waveguide sheet 12,and scattering incident light by the recessed portions 16. Moreover,according to the backlight unit 11, since the optical waveguide sheet 12includes as the sticking preventive means: the plurality of annularraised portions 17 each provided around each of the plurality ofrecessed portions 16 and projecting toward the back face side; and theplurality of protruding portions 18 provided scatteredly in a regionwhich does not include the annular raised portions 17, the opticalwaveguide sheet 12 abuts the reflection sheet 14 or the like disposed onthe back face side of the optical waveguide sheet 12 at dispersed pointsby way of the plurality of annular raised portions 17 and the pluralityof protruding portions 18, whereby adhesion of the back face of theoptical waveguide sheet 12 to the reflection sheet 14 or the like can beinhibited. Therefore, the backlight unit 11 can inhibit rays of lightfrom entering such an adhering portion to give rise to the lack inuniformity of luminance, and additionally it is not necessary toseparately provide a sticking preventive layer on the back face of theoptical waveguide sheet 12, whereby the reduction in thickness can befacilitated. Furthermore, according to the backlight unit 11, due to theannular raised portion 17 formed on the back face of the opticalwaveguide sheet 12 being provided around the recessed portion 16, theadhesion of the recessed portion 16 and the vicinity thereof can beproperly inhibited, and consequently the lack in uniformity of luminancedue to the rays of light scattered by the recessed portion 16 can befavorably inhibited.

Due to including the backlight unit 11 that includes the opticalwaveguide sheet 12, the portable terminal 1 can substantially uniformlyemit rays of light from the front face of the optical waveguide sheet12, and additionally the sticking of the optical waveguide sheet 12 tothe reflection sheet 14 or the like disposed on the back face side ofthe optical waveguide sheet 12 can be inhibited, as described above.Moreover, due to including the backlight unit 11 that includes theoptical waveguide sheet 12, the portable terminal 1 can facilitate thereduction in thickness.

The method for producing an optical waveguide sheet according to theembodiment of the present invention enables the optical waveguide sheet12 to be easily and reliably produced which includes on the back faceside thereof, the plurality of recessed portions 16 falling toward thefront face side, and as the sticking preventive means: the plurality ofannular raised portions each provided around each of the plurality ofrecessed portions 16 and projecting toward the back face side 17; andthe plurality of protruding portions 18 provided scatteredly in a regionwhich does not include the annular raised portions 17.

Since the mold according to the embodiment of the present inventionincludes, on the surface thereof, a reversal shape of the plurality ofrecessed portions provided in a certain pattern, and the plurality ofannular raised portions each provided around each of the recessedportions, the mold can be suitably used as a mold for use in productionof the optical waveguide sheet 12.

The method for producing a mold according to the embodiment of thepresent invention enables a mold to be easily and reliably produced, themold including, on the surface thereof, a reversal shape of theplurality of recessed portions provided in a certain pattern and theplurality of annular raised portions each provided around each of therecessed portions.

Since the master mold according to the embodiment of the presentinvention includes, on the surface thereof, the plurality of recessedportions provided in a certain pattern and the plurality of annularraised portions each provided around each of the plurality of recessedportions, the master mold enables a reversal shape of the plurality ofrecessed portions provided in a certain pattern and the plurality ofannular raised portions each provided around each of the plurality ofrecessed portions to be easily and reliably formed on the surface of amold produced using the master mold.

Other Embodiments

It is to be noted that the optical waveguide sheet, the backlight unit,the portable terminal according to the embodiments of the presentinvention may be exploited in various modified or improved embodimentsother than those as described above. For example, the optical waveguidesheet may not necessarily have a single-layer structure as long as theback face side of the optical waveguide sheet has a predetermined shape,and the optical waveguide sheet may have a multilayer structureincluding two or more layers. Moreover, the optical waveguide sheet mayhave a hard coating layer or the like provided on the front facethereof. Furthermore, the optical waveguide sheet may exhibit alenticular shape or the like on the front face thereof such thatoutgoing rays of light can be controlled. In addition, in order toinhibit the lack in uniformity of luminance in the vicinity of the lightsource, the optical waveguide sheet may have a plurality of V-shaped ortrapezoidal cutaways provided continuously or with a certain spacing onthe end face on the light source side. The arrangement pattern of theprotruding portions and the annular raised portions is not particularlylimited. With respect to the arrangement pattern of the protrudingportions and the annular raised portions, for example, in a case wherethe optical waveguide sheet is used in a bilateral edge-lit backlightunit in which light sources are disposed on both opposing edges, theplurality of protruding portions may be provided such that thearrangement density thereof on the back face gradually decreases fromthe both edges toward the center, and the plurality of annular raisedportions may be provided such that the arrangement density thereof onthe back face gradually increases from the both edges toward the center.

In addition to the methods described above, the production method of theoptical waveguide sheet is also exemplified by a method that involvesusing a mold having, on the surface thereof, merely a reversal shape ofthe plurality of recessed portions provided in a certain pattern. Themethod involving the use of such a mold is exemplified by a method inwhich a plurality of recessed portions are provided on one of the facesof the sheet element constituted from the material for forming anoptical waveguide sheet by using the mold, then a plurality of annularraised portions are each provided around each of the plurality ofrecessed portions by way of a photolithography process and an etchingprocess, and further a plurality of protruding portions are providedscatteredly in a region which does not include the annular raisedportions, by way of the well-known printing process. In addition, themethod for forming a reversal shape of the plurality of recessedportions on the mold is exemplified by a method that involves forming amaster mold having, on the surface thereof, a plurality of recessedportions by way of, for example, a photolithography process and anetching process, and further producing the mold by way of electroformingusing the master mold.

Moreover, the mold may not be necessarily produced by way ofelectroforming using the master mold, and for example, the mold may bedirectly produced using the photolithography process and the etchingprocess, as well as the well-known printing process. In addition, inthis instance, comparatively rigid synthetic resins such aspolycarbonate resins and acrylic resins may be used as the material forforming the mold.

In a case where the optical waveguide sheet is produced using extrusionmolding in which the sheet element is molded by feeding the material forforming an optical waveguide sheet in a molten state to a T-die andextruding the forming material from an extruder and the T-die, one of apair of pressure rollers pressing the extruded sheet element may be usedas the mold having the reversal shape of the plurality of recessedportions and the plurality of annular raised portions each providedaround each of the plurality of recessed portions, and the plurality ofprotruding portions provided scatteredly in a region which does notinclude the annular raised portions. The method for forming such areversal shape on the surface of one of the pressure rollers isexemplified by: a method involving overlaying, on the surface of thepressure roller, a plating layer including, on the surface thereof, areversal shape of the plurality of recessed sections provided in acertain pattern, the plurality of annular raised sections each providedaround each of the recessed sections, and the plurality of protrudingsections provided scatteredly in a region which does not include theannular raised sections; and a method involving forming the reversalshape on the surface of the pressure roller by means of a laser beam orby way of cutting. Moreover, in this instance, a reversal shape of alenticular shape, for example, may be formed on the surface of the otherpressure roller, and consequently the lenticular shape may be formed onthe front face of the optical waveguide sheet.

With respect to the edge-lit backlight unit, disposing the reflectionsheet on the back face side of the optical waveguide sheet is notnecessary, and for example, the front face of the top plate disposed onthe back face side of the optical waveguide sheet may be polished so asto serve as a reflection surface, whereby the reflection surface maysubstitute for the reflection sheet. When the front face of the topplate is formed so as to serve as the rearmost face of the backlightunit in this manner, the edge-lit backlight unit can facilitate thereduction in thickness by omitting the reflection sheet.

The portable terminal is exemplified by various portable terminals suchas the laptop computers described above; mobile phones such assmartphones; personal digital assistants such as tablet terminals; andthe like. Furthermore, the optical waveguide sheet and the edge-litbacklight unit can be used in various liquid crystal display devicessuch as laptop computers whose housing (casing) has a thickness ofgreater than 21 mm, desktop computers and flat-screen televisions, inaddition to the mobile terminal described above.

As described in the foregoing, the optical waveguide sheet, thebacklight unit and the portable terminal according to the embodiments ofthe present invention enable the sticking of the optical waveguide sheetto the reflection sheet, the top plate or the like disposed on the backface side of the optical waveguide sheet to be inhibited withoutseparately providing a sticking preventive layer. Accordingly, theoptical waveguide sheet, the backlight unit and the portable terminalaccording to the embodiments of the present invention can be suitablyused in liquid crystal display devices in which the lack in uniformityof luminance is inhibited and a reduction in thickness is facilitated.

EXPLANATION OF THE REFERENCE SYMBOLS

-   1 portable terminal, ultrathin computer-   2 operation unit-   3 liquid crystal display unit-   4 liquid crystal panel-   5 casing for liquid crystal display unit-   6 top plate-   7 front face support member-   8 hinge part-   9 casing for operation unit-   11 backlight unit-   12 optical waveguide sheet-   13 light source-   14 reflection sheet-   15 optical sheet-   16 recessed portion-   17 annular raised portion-   18 protruding portion-   110 edge-lit backlight unit-   111 optical waveguide sheet-   112 optical sheet-   115 reflection sheet-   116 top plate-   117 light source-   210 edge-lit backlight unit-   211 optical waveguide sheet-   212 optical sheet-   216 top plate-   217 light source

1. An optical waveguide sheet for use in an edge-lit backlight unit, theoptical waveguide sheet having a function of allowing rays of light toenter an end face of the optical waveguide sheet and emitting the raysof light from a front face substantially uniformly, wherein the opticalwaveguide sheet comprises on a back side thereof a sticking preventivemeans; and a plurality of recessed portions falling toward a front faceside, and wherein the sticking preventive means comprises: a pluralityof annular raised portions each provided around each of the plurality ofrecessed portions and projecting toward the back face side; and aplurality of protruding portions provided scatteredly in a region whichdoes not comprise the annular raised portions.
 2. The optical waveguidesheet according to claim 1, wherein the optical waveguide sheet is foruse as a light guide film having an average thickness of no less than100 μm and no greater than 600 μm.
 3. The optical waveguide sheetaccording to claim 1, wherein an average height (H₃) of the protrudingportions from a back face on average level is no less than 2 μm and nogreater than 7 μm.
 4. The optical waveguide sheet according to claim 1,wherein the protruding portions have a height ratio (H₃/D₃) of anaverage height (H₃) to an average diameter (D₃) at a back face onaverage level of no less than 0.05 and no greater than 0.5.
 5. Theoptical waveguide sheet according to claim 1, wherein an average heightof the annular raised portions from a back face on average level is noless than 0.1 μm and no greater than 6 μm.
 6. The optical waveguidesheet according to claim 1, wherein the annular raised portions have aheight ratio (H₂/W₂) of an average height (H₂) to an average width (W₂)at an back face on average level of no less than 0.04 and no greaterthan 0.8.
 7. The optical waveguide sheet according to claim 1, whereinan arrangement pattern of the protruding portions is formed such that aarrangement density of the protruding portions on the back facegradually increases from a first end to a second end, and an arrangementpattern of the annular raised portions is formed such that a arrangementdensity of the annular raised portions on the back face graduallydecreases from the first end to the second end.
 8. The optical waveguidesheet according to claim 1, comprising a polycarbonate resin as aprincipal component.
 9. An edge-lit backlight unit comprising: theoptical waveguide sheet according to claim 1; and a light source thatemits rays of light toward an end face of the optical waveguide sheet.10. A portable terminal comprising the backlight unit according to claim9 in a liquid crystal display unit.